Laboratory of Environmental Toxicology, Ghent University, Ghent, Belgium.
Environ Sci Technol. 2012 Jan 17;46(2):1178-84. doi: 10.1021/es203140p. Epub 2011 Dec 28.
Recent studies have suggested that exposure of the freshwater invertebrate Daphnia magna to dietary Zn may selectively affect reproduction without an associated increase of whole body bioaccumulation of Zn. The aim of the current research was therefore to investigate the hypothesis that dietary Zn toxicity is the result of selective accumulation in tissues that are directly involved in reproduction. Since under field conditions simultaneous exposure to both waterborne and dietary Zn is likely to occur, it was also tested if accumulation and toxicity under combined waterborne and dietary Zn exposure is the result of interactive effects. To this purpose, D. magna was exposed during a 16-day reproduction assay to Zn following a 5 × 2 factorial design, comprising five waterborne concentrations (12, 65, 137, 207, and 281 μg Zn/L) and two dietary Zn levels (49.6 and 495.9 μg Zn/g dry wt.). Tissue-specific Zn distribution was quantified by synchrotron radiation based confocal X-ray fluorescence (XRF). It was observed that the occurrence of reproductive inhibition due to increasing waterborne Zn exposure (from 65 μg/L to 281 μg/L) was accompanied by a relative increase of the Zn burdens which was similar in all tissues considered (i.e., the carapax, eggs, thoracic appendages with gills and the cluster comprising gut epithelium, storage cells and ovaries). In contrast, the impairment of reproduction during dietary Zn exposure was accompanied by a clearly discernible Zn accumulation in the eggs only (at 65 μg/L of waterborne Zn). During simultaneous exposure, bioaccumulation and toxicity were the result of interaction, which implies that the tissue-specific bioaccumulation and toxicity following dietary Zn exposure are dependent on the Zn concentration in the water. Our findings emphasize that (i) effects of dietary Zn exposure should preferably not be investigated in isolation from waterborne Zn exposure, and that (ii) XRF enabled us to provide possible links between tissue-specific bioaccumulation and reproductive effects of Zn.
最近的研究表明，淡水无脊椎动物大型溞暴露于膳食锌中可能会选择性地影响繁殖，而不会导致全身锌生物积累增加。因此，当前研究的目的是验证以下假设，即膳食锌毒性是由于直接参与繁殖的组织中选择性积累的结果。由于在野外条件下，同时暴露于水相和膳食锌中很可能发生，因此还测试了在水相和膳食锌联合暴露下的积累和毒性是否是相互作用的结果。为此，采用 5×2 析因设计，用 5 种水相浓度（12、65、137、207 和 281μg Zn/L）和 2 种膳食锌水平（49.6 和 495.9μg Zn/g 干重），对大型溞进行了为期 16 天的繁殖试验，以暴露于 Zn 中。通过同步辐射基于共焦 X 射线荧光（XRF）定量了组织特异性 Zn 分布。研究发现，由于水相 Zn 暴露增加（从 65μg/L 增加到 281μg/L）而导致的生殖抑制的发生伴随着 Zn 负荷的相对增加，在所考虑的所有组织中都相似（即甲壳、卵、带鳃的胸肢以及包含肠上皮、储存细胞和卵巢的簇）。相比之下，在膳食 Zn 暴露期间，生殖受损伴随着卵中明显可辨的 Zn 积累（在水相 Zn 为 65μg/L 时）。在同时暴露期间，生物积累和毒性是相互作用的结果，这意味着膳食 Zn 暴露后的组织特异性生物积累和毒性取决于水中的 Zn 浓度。我们的研究结果强调，（i）最好不要将膳食 Zn 暴露的影响与水相 Zn 暴露孤立地进行研究，并且（ii）XRF 使我们能够提供 Zn 的组织特异性生物积累与生殖效应之间的可能联系。
